German Published Patent Application No. 28 24 190 (corresponding to U.S. Pat. No. 4,267,569) describes a process and equipment for controlling an internal combustion engine. The aforementioned reference describes two schemes for verifying the operation of an engine control device. In one scheme, a diagnostic subprogram is stored in an auxiliary storage space. When this diagnostic subprogram is run, different test points are polled and their responses checked. In another scheme, diagnostic means are provided that have a control device and a storage device. In this embodiment, the diagnostic subprogram is stored only in the storage device of the diagnostic means and is processed by said means.
The aforementioned schemes have the disadvantage that considerable storage space is needed, or the external diagnostic means can only be used for a certain control device type. If modifications are to be made, especially during the diagnostic procedure, the entire control device must be modified, in the case of the first scheme, or the diagnostic means must be fully reconfigured, in the case of the second scheme.